Who can rain on the Rafa-and-Roger Wimbledon parade?

Where to begin with a rivalry that has captured the imagination with every step through its 20 meetings on the tennis stage?

It is no accident that Roger Federer and Rafael Nadal have shared the top two ATP rankings for more than five years -give or take three months at the start of 2010. In that time, they have only met in semi-finals or finals and, since 2006, have been the last men standing in seven Grand Slam finals and in eight Masters finals.

At Wimbledon, Federer has appeared in the last seven finals and against Nadal in three of them. And Federer’s only loss was to Nadal in the near-iconic 2008 final.

The stakes this time round, though, are higher than ever. Federer lost his top ranking to Nadal with his French Open title. To stand a chance of regaining No.1 this year, he needs to defend the Wimbledon title. Nadal was unable to play last year so this, in effect, is the defence of his title.

There is, however, a different flavour to this year’s event. Federer has suffered a succession of defeats since his victory in Australia, and to players who have always suffered at his hands: Marcos Baghdatis, Tomas Berdych, Ernests Gulbis, Albert Montanes, Robin Soderling and, only last week, Lleyton Hewitt.

Federer talks an upbeat game, and rightly so. His grass game is one of the finest of the Open era. But his aura is slightly tarnished, and that is dangerous.

Nadal, conversely, is enjoying one of his finest ever streaks: three straight Masters titles followed by the French Open. He has come back from injury with a retooled, smarter game, a better serve, more variety, more incisive attack and, if it’s possible, better defence. Can anyone, even Federer, deny him his favourite title?

The draw looks pretty favourable, and even more so now that the first seed in his segment, the dangerous Gulbis, has withdrawn. Nadal could meet James Blake in the second round, but the now-unseeded American, once such a dangerous attacking player, is sadly lacking in form.

A rather larger challenge waits in the fourth round, where Nadal could face John Isner, who has no record on grass, or Mikhail Youzhny. The latter has had a good year so far, but he has lost to the Spaniard at the fourth round stage in both 2007 and 2008, and this year’s Nadal is a different and tougher prospect.

It’s in the quarterfinals that the fun may begin. Soderling will almost certainly out-play David Ferrer -who has never got beyond the fourth round at Wimbledon -for a chance to wreak revenge on his Roland Garros loss to Nadal. His big serve and ground game, particularly if it’s warm and dry, will be tough, but Nadal’s defence, and superior mobility and touch around the net, should see him through.

His reward may be Andy Murray, but the Great British hope has his own tricky draw to negotiate. It should be plain sailing until the fourth round, where he could meet last week’s Queens winner, Sam Querrey. As an aside, the American has an interesting hurdle in his first round: Sergiy Stakhovsky has just won the Unicef Open in the Netherlands without dropping a set. That one could be fireworks.

In the quarters, Murray is likely to face -and should beat -Fernando Verdasco or Jo-Wilfried Tsonga, for a place against Nadal.

Murray ought to see this as a relatively benign draw. Federer, who has beaten him in two Slam finals, Roddick, who beat him here last year, and a resurgent Hewitt are in the other half. Meanwhile, Murray has beaten Nadal in their last two Slam meetings. The stars may be in alignment.

And so to Federer. His biggest early challenge is Feliciano Lopez, who has an ideal grass court game, but he retired with injury this week in Eastbourne. The other early danger is Jurgen Melzer, who’s enjoying some good form, but cannot manipulate the grass like Federer.

Other pitfalls ahead of the semis? Berdych has both the power game and some ability on grass, but he has to get past Stan Wawrinka and then Nikolay Davydenko, who’s playing his first major tournament since March. Neither is at their best on grass, however, and it’s just possible that a sleeper like Denis Istomin, who made waves both at Queens and at Eastbourne, could be the surprise quarter-finalist.

Federer then meets the survivor of possibly the toughest quarter, topped by Novak Djokovic. The No.3 seed could meet the dangerous Gael Monfils or the Halle-winning, Federer-defeating Hewitt in the fourth round. By the quarters, it may be three-time Wimbledon finalist Andy Roddick, but he will have to beat another dangerous sleeper, Mardy Fish: a slimmer, faster, fitter and more confident player than he’s ever been, and with just the game for grass.

So calling who Federer might meet ahead of Nadal is tricky but, on balance, it may be a rematch of last year’s final against Roddick.

So the Andys versus the big R’s. And no one ought to bet their house on the Andys not prevailing this time. What odds on a British winner, then?